The concept of data hiding or containment is well-known in computer science. The motivation for data hiding is to reduce dependency between the environment, internal structure and the code that manipulates it. Illegally accessing hidden data usually results in a compile-time or run-time error.
Data hiding is a characteristic of object-oriented programming. Because an object can only be associated with data in predefined classes or templates, the object can only “know” about the data it needs to know about, eliminating the possibility that someone maintaining the code may inadvertently point to or otherwise access the wrong data unintentionally.
It is sometimes desirable, however, to provide some of this hidden data to an isolated object, while maintaining the object's isolation. It would be helpful if there were a way to provide hidden data to an isolated object without destroying the object's isolation.